GB2454062A

GB2454062A - Controlling propulsion of a hybrid vehicle according to coolant temperature

Info

Publication number: GB2454062A
Application number: GB0816927A
Authority: GB
Inventors: Khang T Hong; William David Treharne; Paul Stephen A Bryan; Shunsuke Okubo
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2007-10-23
Filing date: 2008-09-16
Publication date: 2009-04-29
Anticipated expiration: 2028-09-16
Also published as: US20090105037A1; CN101417618A; CN101417618B; GB2454062B; US7789794B2; GB0816927D0

Abstract

A hybrid or alternatively powered vehicle has a propulsion system including an electric machine, e.g. motor/generator 20, 22, power electronics e.g. inverters 24, 26 and a coolant 32 to cool the electric machine and power electronics. The temperature of the coolant and the power electronics is measured and the difference between them determined and compared to an expected temperature difference. The maximum output torque of the electric machine is reduced if the actual temperature difference is greater than the expected temperature difference. The expected temperature difference may take into account: the ambient temperature; a torque command for the electric machine; vehicle speed.

Description

CONTROLLING A PROPULSION SYSTEM

OF AN ALTERNATIVELY POWERED VEHICLE

Field of the invention

The invention relates to methods and systems for controlling propulsion systems of alternatively powered vehicles.

Background of the invention

Various methods are used to detect anomalous operating states of vehicle systems. U.S. Pat. No. 6,009,362 to Furukawa is an example of such a method. According to Furukawa, an anomalous condition detecting apparatus includes a detector for detecting a pair of positive and negative terminals of a fan motor. The apparatus also includes a decision circuit for deciding whether an anomalous condition exists based on a voltage detected between the terminals. An external resistor is provided between the positive terminal of the motor and a power source. The negative terminal of the motor is earthed. A voltage between the terminals is detected. The decision circuit decides that an anomalous condition exists when the potential of the positive terminal is smaller than a predetermined value.

U.S. Pat. No. 6,377,880 to Kate et al. is another example of such a method. According to Kato et al., a cooling fan failure detection apparatus for a hybrid vehicle comprises a cooling capacity calculation device, which calculates a cooling capacity of a cooling fan, a battery heating value calculation device, which calculates a heating value of a battery, and an assumed temperature change calculating device, which calculates an assumed temperature change of the battery based on the heating value and the cooling capacity. The apparatus further comprises an actual temperature change calculating device, which calculates an actual temperature change of the battery, and a failure determination device. The failure determination device determines whether the cooling fan is failing by comparing the assumed temperature change and the actual temperature change.

Wa 2006/095929 to Yanagida is yet another example of such a method. According to Yanagida, a start control repeatedly performs a start-up process for a start of an oil pump. In the event of a failed start-up of the oil pump by repetition of the start-up process, the start control specifies the occurrence of an abnormality in the oil pump or in the power supply to the oil pump at an outside air as temperature that is not lower than a present reference temperature.

Summary of the invention

In accordance with a first aspect of the invention, there is provided a method for controlling a propulsion system of an alternatively powered vehicle, the propulsion system including an electric machine having a maximum output torque, power electronics to control the electric machine and a coolant to cool the electric machine and power electronics, which method comprises determining an expected temperature difference between the coolant and the power electronics; determining an actual temperature difference between the coolant and the power electronics; determining whether the actual temperature difference is greater than the expected temperature difference; and reducing the maximum output torque of the electric machine if the actual temperature difference is greater than the expected temperature difference.

Conveniently, the maximum output torque of the electric machine is reduced by an amount based on the difference between the actual temperature difference and the expected temperature difference.

In accordance with a second aspect of the invention, there is provided a hybrid electric vehicle propulsion system as hereinafter set forth in Claim 7 of the appended claims.

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which Figure 1 is a plot of a ratio of a maximum motor/generator torque command at a present vehicle speed versus an inverter temperature, coil temperature and oil temperature, Figure 2 is a block diagram of a portion of a hybrid electric automotive vehicle, Figure 3 is a block diagram of the transaxle of Figure 2.

Figure 4 is flow chart of a strategy for detecting whether an inverter is functioning as designed in accordance with certain embodiments of the invention, Figure 5 is a plot of a temperature difference between one of the inverters of Figure 3 and the fluid in the cooling line of Figure 3 versus a torque command for a given ambient temperature, Figure 6 is a flow chart of a strategy for managing a motor electronics cooling system in accordance with certain embodiments of the invention, arid Figure 7 is a plot of a ratio of a maximum motor/generator torque command at a present vehicle speed versus an inverter temperature.

Detailed description of the preferred embodiment(s) Strategies and techniques are described herein with reference to an alternatively powered vehicle having a power split hybrid transaxie with two electric machines. The strategies and techniques described herein, however, may be applied to other alternatively powered vehicles having any number of electric machines. As an example, the strategies and techniques described herein may be applied to a parallel hybrid vehicle having a single electric machine. As another example, the strategies and techniques described herein may be applied to a series hybrid vehicle having four electric machines.

A motor electronics cooling system (MECS) for a power split hybrid transaxle may use a liquid cooling system driven by an electric pump to transfer heat generated from the transaxle to the atmosphere. This system uses a coolant-to-air radiator design which may be similar to that used for an internal combustion engine.

When the MECS is functioning as designed, it is able to provide sufficient cooling to the inverters, motor/generator coils, and transmission fluid. Under certain operating conditions, the inverters, coils, and/or transmission fluid may reach temperatures near their functional limits. To prevent the transaxle components from exceeding their functional limits, a transmission control unit (TCU) may reduce the amount of torque output depending on the actual temperature of its components. As may be seen in the example of Figure 1, a ratio of a maximum motor/generator torque command at a present vehicle speed is reduced beyond certain threshold inverter temperatures (as indicated by heavy solid line), coil temperatures (as indicated by light solid line) and oil temperatures (as indicated by dashed line) . This torque reduction strategy permits the transaxle components to cool down before allowing the vehicle to return to full drivability.

When the MECS is not functioning as designed, for example if there is an incorrect coolant type in the system, the above torque reduction strategy may not cool the transaxle components quickly enough to allow a return to full vehicle drivability. As an example, the power electronics of the inverters may quickly transition from a normal temperature to a maximum temperature. At this maximum temperature limit, the TCU may put the vehicle into a limited operating state (LOS) or quit on road (QOR) condition depending on whether the motor's electronics or the generator's electronics have surpassed their limits.

Detection and management strategies described herein may be similar for a motor inverter and a generator inverter. Each inverter, however, may be independently evaluated. The time at which torque reduction begins to occur may be independently controlled. By separating the detection and management of each inverter, vehicle drivability may be maximized. As an example, at highway cruising speeds, the generator provides a greater amount of torque as compared to the motor. This may cause the generator to achieve a temperature at which it no longer functions as designed. As another example, under steep grade conditions, the motor provides a greater amount of torque as compared to the generator. This may cause the motor to achieve a temperature at which it no longer functions as designed.

As may be seen in the example of Figure 2, a hybrid control unit (HCU) 10 communicates with an ambient temperature sensor 12, engine control unit (ECU) 16 and a transaxie 18 including a power electronics module (PEN) 19.

As indicated above, other configurations are also possible.

As may be seen in the example of Figure 3, the transaxle 18 includes a motor 20 and a generator 22. In other examples, the transaxie may include a smaller or greater number of electric machines. The PEM 19 includes motor and generator inverters 24, 26 and temperature sensors 28, 30 which monitor the temperatures of the motor and generator inverters 24, 26 respectively. A cooling line 32 of a MECS passes through the transaxle 18. The cooling line 32 carries a fluid to cool the motor 20 and generator 22 and motor and generator inverters 24, 26. A temperature sensor 34 monitors the temperature of the fluid of the cooling line 32.

Detection Some of the detection strategies herein are based on the linearly dependent relationship between torque outputs of the motor 20 and generator 22 and a temperature rise of the inverters 24, 26 over a temperature of the fluid of the cooling line 32, referred to herein as INVDELTAT. As may be seen in the example of Figure 4, at block 36, the HCU 10 determines whether the temperature sensors 12, 28, 30, 34 are functioning as designed. If no, the strategy returns to Begin. The operation of the temperature sensors 12, 28, 30, 34 may then be remediated in any suitable fashion. If yes, the HCU 10 determines, at block 38, a predicted temperature difference between each of the inverters 24, 26 and the temperature of the fluid of the cooling line 32. The predicted temperature differences are based on the ambient temperature and respective torque commands for the motor 20 and generator 22, which are linearly proportional with the torque outputs of the motor 20 and generator 22 respectively. In other examples, the predicted temperature may be based on factors such as a cooling fan speed and vehicle speed. To make this determination, the HCU 10, for example, may consult a look-up table stored in memory populated with such data. This data may be gathered via testing, simulation or any other desired technique.

At block 40, the HCU 10 determines whether either of the actual temperature differences between the inverters 24, 26 and the temperature of the fluid of the cooling line 32 is greater than its respective predicted temperature difference. The HCU 10, for example, reads the temperature sensors 28, 30, 34 to calculate the actual temperature differences. If no, the HCU 10, at block 42, decrements a counter unless the counter is equal to zero. The strategy then returns to Begin. If yes, the HCU 10, at block 44, increments the counter. At block 46, the HCU 10 determines if the counter has reached its maximum value. This maximum value may be calibratable and depend on design considerations. If no, the strategy returns to Begin. If yes, a cooling flag is set at block 48. The strategy then proceeds to End.

As may be seen in the example of Figure 5, the circular data points indicate measured INVDELTAT, at various torque commands for the motor 20, when the MECS is functioning as designed. The square data points indicate measured INVDELTAT, at various torque commands for the motor 20, when the MECS is not functioning as designed. Similar data may be obtained via analysis, testing or simulation for generator 22. The lower line is selectively drawn to indicate the minimum predicted INVDELTAT. The upper line is selectively drawn to indicate the maximum predicted INVDELTAT. The lower line may be the calibratable limit at which the counter discussed above is incremented or decremented.

As discussed below, a percentage of torque reduction may be calculated as a linear interpolation of the actual INVDELTAT relative to the upper and lower lines of Figure 5. For example, a lesser amount of torque reduction

-B-

may occur when temperature differences are closer to the lower line. A greater amount of torque reduction may occur when temperature differences are closer to the upper line.

Other techniques may also be used to determine the percentage of torque reduction. As an example, a single line may be selectively drawn on Figure 5 to indicate the predicted INVDELTAT. The percentage of torque reduction may be a fixed amount that is applied when the actual INVDELTAT exceeds the predicted INVDELTAT.

Management In the example of Figures 2 and 3, most of the power loss from the inverters 24, 26 is dissipated in the form of heat. The amount of power loss increases as the electrical power output of the inverters 24, 26 increases. The amount of torque output by the motor 20 and generator 22 is proportional to the electrical power output of the inverters 24, 26 respectively. If functioning properly, the heat generated by the inverters 24, 26 is equal to or less than the amount of heat that may be dissipated by the NECS. If not functioning properly, the heat generated by the inverters 24, 26 may be greater than the amount of heat that may be dissipated by the MECS. Limiting the amount of torque output by the motor 20 and generator 22 limits the heat generated by the inverters 24, 26 respectively.

As may be seen in the example of Figure 6, at block 50, the HCU 10 determines whether the cooling system flag has been set. If no, the strategy returns to Begin. If yes, the HCU 10, at block 52, determines if the actual temperature differences of the inverters 24, 26 are beyond the limit for a cooling system not functioning as designed.

If no, the strategy returns to block 50. If yes, the HCU 10, at block 54, sets a diagnostic code and illuminates a wrench. At block 56, the HCU 10 reduces the maximum allowable torque. The strategy then proceeds to End.

In the example of Figure 6, the amount of torque reduction depends on the actual INVDELTAT relative to the minimum and maximum predicted INVDELTAT. As an example, if torque reduction is warranted and the actual INV_DELTA_T is halfway between the minimum and maximum predicted INVDELTAT of Figure 5, then, as may be seen in the example of Figure 7, the HCU 10 may reduce the ratio of motor torque command at the present vehicle speed from 100% to a value halfway between the solid and dotted lines, or 80%, for motor inverter temperatures between approximately 75 and 140 Celsius. The solid line indicates the minimum torque reduction calibrated when the MECS is not functioning as designed. The dotted line indicates the maximum torque reduction calibrated when the MECS is not functioning as designed. The closer the actual INVDELTAT is to the minimum predicted INV DELTA TI the lesser the torque reduction. If the actual INVDELTAT is equal to or greater than the maximum predicted INVDELTAT, the HCU 10 will reduce the torque by 100% of the calibrated table of Figure 7.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the scope of the invention as set out in the appended claims.

Claims

-10 - CLAIMS

1. A method for controlling a propulsion system of an alternatively powered vehicle, the propulsion system including an electric machine having a maximum output torque, power electronics to control the electric machine and a coolant to cool the electric machine and power electronics, the method comprising: determining an expected temperature difference between the coolant and the power electronics; determining an actual temperature difference between the coolant and the power electronics; determining whether the actual temperature difference is greater than the expected temperature difference; and reducing the maximum output torque of the electric machine if the actual temperature difference is greater than the expected temperature difference.

2. A method as claimed in claim 1, wherein the expected temperature difference takes into account an ambient temperature.

3. A method as claimed in claim 1 or 2, wherein the expected temperature difference takes into account a torque command for the electric machine.

4. A method as claimed in claim 1 or 2, wherein the expected temperature difference takes into account vehicle speed.

5. A method as claimed in any preceding claim, which further comprises incrementing a counter if the actual temperature difference is greater than the expected temperature difference and determining whether the counter has exceeded a threshold wherein the maximum output torque of the electric machine is reduced if the counter has exceeded the threshold.

-11 -

6. A method as claimed in any preceding claim, wherein the maximum output torque of the electric machine is reduced by an amount based on the difference between the actual temperature difference and the expected temperature difference.

7. A hybrid electric vehicle propulsion system comprising: an electric machine having a maximum output torque; power electronics to control the electric machine; a coolant to cool the electric machine and power electronics; and one or more controllers configured to * determine an expected temperature difference between the coolant and the power electronics, * determine an actual temperature difference between the coolant and the power electronics, * determine whether the actual temperature difference is greater than the expected temperature difference, and * reduce the maximum output torque of the electric machine if the actual temperature difference is greater than the expected temperature difference.

8. A system as claimed in claim 7, wherein the expected temperature difference is based on an ambient temperature.

9. A system as claimed in claim 7 or 8, wherein the expected temperature difference is based on a torque command for the electric machine.

10. A system as claimed in claim 7 or 8, wherein the expected temperature difference is based on a vehicle speed.

11. A system as claimed in any one of claims 7 to 10, wherein the one or more controllers are further configured -12 -to increment a counter if the actual temperature difference is greater than the expected temperature difference and to determine whether the counter has exceeded a threshold and wherein the maximum output torque of the electric machine is reduced if the counter has exceeded the threshold.

12. A system as claimed in any one of claims 7 to 11, wherein the maximum output torque of the electric machine is reduced by an amount based on the difference between the actual temperature difference and the expected temperature difference.

13. A method for controlling a propulsion system of an alternatively powered vehicle, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.